A well known and widely used procedure for diagnosing damage to the ligaments and muscles of an anatomical joint in the skeletal structure of the body has been to apply forces against the body and observe the resultant response. The premise is that upon application of a properly applied force to the body structure, several factors can be observed to form the basis for a valid diagnosis. These factors include: 1) the resistance encountered; 2) the extent of relative bone movement; and 3) the nature of the resultant joint movement. Heretofore, however, the procedures which have been used are somewhat unreliable and inconclusive. In most instances the force has been applied by simple manipulation of the suspected joint. Importantly, this manipulation has been without knowledge of the exact magnitude of the applied force and without certainty as to the direction of the force or the point at which the force has been applied. Consequently, conclusions have been subjectively ascertained. As such, they are based on inconsistencies and subject to question.
It is clear that more accurate conclusions about the health of joint ligaments and muscles could be made if the testing procedures were more standardized and more accurately performed. For the type of testing envisioned by the present invention this requires that the magnitude and direction of the applied force, as well as its point of application, all be accurately determined. Further, once the force application is accurately quantified, the extent of any resultant movement in the anatomical structure of the body needs to be accurately measured. To do this is not a simple matter. Certainly it is not a procedure which can be repetitively duplicated with consistency by simple manipulation. The consequence has been a growing recognition that mechanical devices and apparatus can be used to obtain the consistency and accuracy that is otherwise elusive.
As is well known, the body has many joints, and all are anatomically different. Not only will the set up for applying a force against a joint be different, the various joints will themselves react differently to the applied force. Consequently, each joint should be considered separately, on its own. With this in mind, consider the knee. An example of a device which has been specifically designed and engineered to assist the physician in diagnosing the health of ligaments and muscles in a knee joint is the device which is claimed and disclosed in U.S. Pat. No. 4,969,471 (hereinafter the '471 patent). The '471 patent which issued to Daniel et al. for an invention entitled "Knee Ligament Testing Device and Method of Use" is assigned to the assignee of the present invention. Unlike the device disclosed in the '471 patent, however, the present invention is concerned with the shoulder.
The ligaments and muscles of the shoulder can be tested by examining the movement and displacement of the humeral head relative to the scapulae and clavicle. To do this, it is preferable if both the clavicle and the scapular spine can be held stationary. Once the clavicle and scapular spine have been fixed and are held in place, a force is then applied to the humeral head to move the humeral head. As indicated above, with knowledge of the exact magnitude of the applied force, and with certainty as the direction in which the force is applied against the humeral head, a measurement of humeral head movement and displacement relative to the scapulae and clavicle will provide a valid basis for diagnosing the health of the ligaments and muscles in the shoulder. Of particular concern is the inferior glenohumeral ligament.
It is known anatomically that both static and dynamic stabilizers serve to reduce potential humeral displacement relative to the scapulae and clavicle. The static stabilizing elements include the glenohumeral ligaments, and the dynamic stabilizers include the overlying rotator cuff. There are three glenohumeral ligaments (superior, middle and inferior) which are formed by localized condensations of the joint capsule fibers and which are the primary static stabilizers when taut. Of these, the inferior glenohumeral ligament is the largest and is thought to play the greatest role in prevention of dislocation.
It happens that the glenohumeral joint is most prone to traumatic subluxation or dislocation when the arm is in the abducted and externally rotated position. In this position, the inferior glenohumeral ligament, which is lax in adduction, becomes taut. Indeed, the inferior glenohumeral ligament gradually tightens as abduction increases such that at 90 degrees it acts as the primary restraint to anterior displacement. With this in mind, any insufficiencies in the inferior glenohumeral ligament can be revealed with proper testing.
In addition to testing the inferior glenohumeral ligaments, as the target structure, an increased capability for testing the shoulder at varying angles will perhaps prove useful in testing secondary restraints. Further, where the subject injury is acute or where pain limits rotation testing to positions other than the preferred position, testing may still be necessary and may still prove diagnostic.
In light of the above it is an object of the present invention to provide an apparatus for testing the shoulder of a patient which can be repetitively used to obtain consistent results. Another object of the present invention is to provide a shoulder tester which will test shoulders with the arm at any angle, (0 to 90 deg.), with the subject sitting or supine, with the arm adducted, abducted or otherwise. It is another object of the present invention to provide an apparatus for testing the shoulder of a patient which accurately directs a force against the humeral head. Yet another object of the present invention is to provide an apparatus for testing the shoulder of a patient which simultaneously measures the magnitude of a force applied against the humeral head and the extent of the resultant movement of the humeral relative to the clavicle. Still another object of the present invention is to provide an apparatus for testing the shoulder of a patient which is simple to use, relatively easy to manufacture and comparatively cost effective.